Sandy, I looked into submitting something to Oprah 5(?) years ago, and that same language was in effect.
What it means is: if I submit a poem, I give up all rights to that poem forever. I can't submit it to another publication, and I can't publish it myself.
With 8 gazillion people submitting poems, the chance of recognition is a dust mote. I'm not worried about rejection -- it's the almost certainty that my poems will be doomed to oblivion and never see the light of day.
Relinquishing ALL rights to my work is not an option, period.